1. Field of the Invention
The present invention relates to a retractable tape measure, and more particularly to a retractable tape measure that can measure longer distances.
2. Description of Related Art
A retractable tape measure is a convenient tool to measure distance. With the reference to the FIG. 3, a conventional retractable tape measure has a base (40), a top cover (not shown) and a calibrated tape (47).
The base (40) has four corners and four sides and includes four supporting bosses (41), a tape slot (401), a pin (43) and a flat coil spring (45). Each supporting boss (41) has a hole (42) and is mounted near a corresponding corner of the base (40). The tape slot (401) is defined through one side of the base (40) near a corner. The pin (43) is mounted in the center of the base (40), and a slot (44) is defined longitudinally in the pin (43). The flat coil spring (45) has an inner end (not numbered) and an outer end (not numbered). A hook (46) is formed on the inner end of the flat coil spring (45) and is securely attached to the slot (44) in the pin (43). The calibrated tape (47) has a proximal end (not numbered) and a distal end (not numbered). The proximal end is attached to the outer end of the flat coil spring (45), and the calibrated tape (47) is wound around the flat coil spring (45). A rigid lip (48) is attached to the distal end of the calibrated tape (47). The rigid lip (48) extends out of and hooks the tape slot (401) to keep the calibrated tape (47) from completely retracting into the base (40) and top cover.
The conventional retractable tape measure is easy to carry, but only a fixed length of calibrated tape (47) can be wound on the flat coil spring (45) attached to the pin (43), and the measuring tape can only measure a distance equal to the length of the calibrated tape (47) at one time. When the distance to be measured is longer than the calibrated tape (47), the retractable tape measure must be used repeatedly and the distances added to obtain the total distance. If the space in the base (40) were able to be fully used to carry a longer calibrated tape (47), the tape measure would be able to measure longer distances in a single operation and be more convenient to use.
To overcome the shortcomings, the present invention provides a means of winding a longer calibrated tape in a retractable tape measure to mitigate or obviate the aforementioned problems.
The primary objective of the present invention is to mount a longer calibrated tape in a given retractable tape measure base. The retractable tape measure in accordance with the present invention uses two internal coil springs and an elliptical belt mounted around the two coil springs. The elliptical belt has a circumference significantly larger than that of a single coil spring of a conventional one. This allows the calibrated tape to be distributed more efficiently inside the retractable tape measure.